The subject matter disclosed herein relates to heating, ventilation and air conditioning (HVAC) systems. More specifically, the subject matter disclosed herein relates to falling film evaporators for HVAC systems.
HVAC systems, such as chillers, use an evaporator to facilitate a thermal energy exchange between a refrigerant in the evaporator and a medium flowing in a number of evaporator tubes positioned in the evaporator. In a flooded evaporator, the tubes are submerged in a pool of refrigerant. This results in a particularly high volume of refrigerant necessary, depending on a quantity and size of evaporator tubes, for efficient system operation. Another type of evaporator used in chiller systems is a falling film evaporator. In a falling film evaporator, the evaporator tubes are positioned typically below a distribution manifold from which refrigerant is urged, forming a “falling film” on the evaporator tubes.
Falling film evaporators commonly employ a distribution system whose function is to convey liquid refrigerant equitably over the falling film tube bundle. The uniformity of liquid refrigerant supplied to the falling film bundle is critical to the performance of a falling film evaporator. One of the more effective approaches uses a separator to separate liquid refrigerant from the liquid-vapor refrigerant mixture that enters the separator. The liquid refrigerant is then drained from the separator and conveyed to a distribution manifold that meters the flow of liquid refrigerant equitably over the evaporator tubes. The separator may be located externally or internally to the evaporator however it is commonly the latter due to the added cost and complexity of the former by way of external piping, packaging and the requirement for the separator to meet pressure vessel certification standards, for example ASME VIII.